This invention pertains to conveyor sortation systems and, in particular, to a method and apparatus for inducting product to a sorter, wherein the sorter includes a continuous conveying member defining a plurality of transport positions and a plurality of sort destinations for receiving product discharged from the continuous member. The invention has application to both linear sorters, such as positive displacement sorters, and carousel sorters, such as tilt-tray and cross-belt sorters.
The quintessential goal for any material-handling system is to maximize the throughput of product through the system. In the case of a sorter, it is known that the throughput of the sorter is limited by the ability of the system to induct product to the sorter at a rate that matches the throughput of the sorter, with adequate gaps between the product. If an insufficient rate of product is supplied to the sorter, then the sorter becomes starved and is incapable of meeting its rated throughput.
A common technique for keeping the sorter supplied with product is to build accumulation into the system upstream of the induct. With a backlog of product at the input to the induct, the function of the induct becomes limited to ensuring that adequate product gaps are developed and, in the case of multiple-line inducts, that the products are merged together from the multiple lines. However, accumulation comes at a cost and is not always feasible. For example, some systems require that substantially all of the conveyors be of the belt variety. This is especially common in the parcel-handling industry where packages may be poorly packaged and may include protruding items from the packages. The use of live-roller conveyors, which are the common form of accumulation, is considered to be inappropriate for handling such parcels. Accordingly, the ability to induct product to the sorter at an adequate rate becomes difficult when accumulation upstream of the sorter is not practical, such as where the conveyors are of the belt variety.
Carousel-type sorter systems are known to be able to handle product of a wide range of characteristics and can be compact and configured in many different ways. In particular, the induct systems and the destination chutes, or conveyors, can be arranged at any place along the carousel and can be arranged on one or both sides of the carousel. In order to provide maximum product throughput with a carousel sorter, empty units are booked, or reserved, for product positioned on the induct. However, a particular timing window must exist in order to accelerate the product to the speed of the carousel to meet the booking requirement for a particular empty carrying unit. If this window cannot be met, it is necessary for the carrier to pass by the induct without a product being loaded on that unit. It should be apparent that the more carriers that pass by the induct without receiving a product, the lower the throughput of the carousel-type sortation system. Conversely, the throughput of a carousel-type sorter can be increased by ensuring a maximum loading of the carriers passing by an induct.